The invention is based on a valve for controlling liquids as defined in more detail by the preamble to claim 1.
From German Patent Disclosure DE 197 328 02, a fuel injection device for internal combustion chambers is known that has a high-pressure fuel source. The fuel injection device has two valve seats, which cooperate with sealing faces of a closing body in a motion sequence upon actuation by a piezoelectric drive; initially, in the closing position, the closing body is located on the first valve seat and is then moved into an intermediate position between the valve seats, and then regains a closing position, but on the second valve seat.
In this way, because of the course of motion of the closing body from one valve seat to the other, a brief relief of a valve control chamber is attained, by way of whose pressure level an opening and closing position of a valve needle in the fuel injection device, which is embodied as force-balanced, is determined, and the fuel injection is thus controlled. The fuel injection is made possible while the closing body is located in an intermediate position between the two valve seats. In this way, the fuel injection is achieved by means of a single excitation of the piezoelectric drive.
Since a time-consuming reversal of motion of the closing body during the fuel injection is not needed, the time losses upon triggering the known fuel injection device are advantageously relatively slight.
However, it has been found that overswings of the closing body occur when the closing body is to be brought to a middle position between the two valve seats. As soon as the closing body swings too far in the direction of the first or the second valve seat, this can adversely cause imprecisions in metering the injection quantity.
It is possible for the middle position of the closing body between the valve seats to be stabilized by spring force, but that has the disadvantage that the piezoelectric drive would have to be moved counter to the spring force into its closing position on the second valve seat. Accordingly, the piezoelectric drive would have to be made correspondingly large, thus adversely affecting production costs and the structural dimensions of the injection device.
The object of the invention is to create a valve for controlling liquids with which the aforementioned disadvantages, and especially overswings in the middle position of the valve closing member, are avoided.
The valve of the invention for controlling liquids, having the characteristics of claim 1, has the advantage that the control motions of the valve member are damped by damping devices in such a way that the valve closing member is stabilized in its middle position between the two valve seats. Accordingly, even high-frequency injections of liquids, especially fuel, through the valve of the invention can be performed exactly, without leading to fluctuations in the injection quantity from overswings of the valve closing member into an unfavorable intermediate position.
In the valve of the invention, the damping devices generate hydraulic forces that briefly act counter to the direction of motion of the valve closing member and thus suitably slow it down into a middle position between the two valve seats. Accordingly, the valve closing member can reach its stable middle position without the incidence of overswings.
A significant advantage of the invention is also that the hydraulic counterforces generated by the damping devices act only briefly, and so the piezoelectric unit does not move the valve closing member into the closing position toward the second valve seat counter to these damping forces. The piezoelectric unit can thus be correspondingly small in size, which reduces the production costs.
Further advantages and advantageous features of the subject of the invention can be learned from the specification, drawing and claims.